Heat exchanger assembly

ABSTRACT

An apparatus and method of forming a hybrid heat exchanger including a first manifold defining a first fluid inlet and a second manifold defining a second fluid inlet. A monolithic core body includes a first set of flow passages in fluid communication with the first manifold and a second set of flow passages is in communication with the second manifold. At least a portion of the first manifold or the second manifold has a tunable coefficient of thermal expansion that is less than a coefficient of thermal expansion of the structurally rigid monolithic core.

BACKGROUND

Contemporary engines used in aircraft produce substantial amounts ofheat that must be transferred away from the engine in one way oranother. Heat exchangers provide a way to transfer heat away from suchengines.

Oil can be used to dissipate heat from engine components, such as enginebearings, electrical generators, and the like. Heat is typicallytransferred from the oil with heat exchangers to maintain oiltemperatures at a desired range from approximately 100° F. to 300° F. Inmany instances, an external environment can be as low as −65° F. or thetemperature of the aircraft fuel can be significantly lower than the oiltemperatures. In such an example, a flow of cool air can be used to coolthe oil at the heat exchanger with force convection. For example, hightemperature (>700° F.) and high pressure bleed air can be cooled withambient bypass air. Other applications utilize air, fuel, and oil toboth cool and heat one another, depending on the need.

Additionally, heat exchangers can be placed in the aircraft fordissipating heat generated by electrical systems, such as within anavionics chassis. The heat exchangers can include a plurality ofelements, such as conduits, to draw heat from the electrical components.The heat exchanger can be used to dissipate the heat drawn from theelectrical components.

BRIEF DESCRIPTION

In one aspect, the present disclosure relates to a method of forming aheat exchanger including: forming a monolithic core having a first setof flow passages; and additively manufacturing onto the monolithic corea first manifold, where the first manifold defines a first fluid inletthat is in fluid communication with the first set of flow passages andat least a portion of the first manifold has a coefficient of thermalexpansion less than a coefficient of thermal expansion of the monolithiccore.

In another aspect, the present disclosure relates to a method of forminga heat exchanger including: forming a monolithic core having a first setof flow passages from a first material having a first coefficient ofthermal expansion; and additively manufacturing a first manifold from asecond material different than the first material onto the monolithiccore in fluid communication with the first set of low passages having asecond coefficient of thermal expansion lower than the first coefficientof thermal expansion.

In yet another aspect, the present disclosure relates to a heatexchanger including monolithic core body having a first set of flowpassages and a first coefficient of thermal expansion. A first manifoldis unitarily formed with the monolithic core body in fluid communicationwith and defining a first fluid inlet for the first set of flowpassages, and having a second coefficient of thermal expansion that isdifferent than the first coefficient of thermal expansion.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a perspective view of an aircraft having a heat exchangerprovided in an aircraft engine, in accordance with various aspectsdescribed herein.

FIG. 2 is a perspective view of a heat exchanger that can be used in theaircraft of FIG. 1.

FIG. 3 is a schematic view of the heat exchanger of FIG. 1 having afirst manifold and a second manifold coupled to a core, in accordancewith various aspects described herein.

FIG. 4 is a plot graph illustrating the coefficient of thermal expansionfor electroformed portions of the heat exchanger of FIG. 2, plottedagainst atomic nickel concentration for five different operatingtemperatures of the electroformed portions, in accordance with variousaspects described herein.

FIG. 5 is a flow chart illustrating a method of forming a heat exchangersuch as the heat exchanger of FIG. 1.

FIG. 6 is a schematic view of an electroforming bath including the heatexchanger core and a sacrificial anode, in accordance with variousaspects described herein.

FIG. 7 is a schematic view of an electroforming bath including the heatexchanger core of FIG. 6 with sacrificial portions prepared forelectroforming the first and second manifolds of FIG. 2, in accordancewith various aspects described herein.

FIG. 8 is a perspective view of the heat exchanger core of FIG. 7,including electroformed manifolds formed onto the core, in accordancewith various aspects described herein.

DETAILED DESCRIPTION

Aspects of the disclosure described herein are directed to a heatexchanger assembly having different coefficients of thermal expansion toreduce thermal stress. For purposes of illustration, the presentdisclosure will be described with respect to a heat exchanger providedin the interior of an aircraft engine. It will be understood, however,that aspects of the disclosure described herein are not so limited andmay have general applicability within any environment requiring orutilizing heat exchangers or convective heat transfer, such as within aturbine engine for the aircraft, but also including non-aircraftapplications, such as other mobile applications and non-mobileindustrial, commercial, and residential applications.

As used herein, the term “forward” or “upstream” refers to moving in adirection being relatively closer to an inlet or source of a flow offluid or gas through a heat exchanger. The term “aft” or “downstream”refers to a direction being relatively closer to an outlet or end of aheat exchanger. As used herein, the term “set” can refer to one or moreof an element. All directional references (e.g., radial, axial,proximal, distal, upper, lower, upward, downward, left, right, lateral,front, back, top, bottom, above, below, vertical, horizontal, clockwise,counterclockwise, upstream, downstream, forward, aft, etc.) are onlyused for identification purposes to aid the reader's understanding ofthe present disclosure, and do not create limitations, particularly asto the position, orientation, or use of aspects of the disclosuredescribed herein. Connection references (e.g., attached, coupled,connected, and joined) are to be construed broadly and can includeintermediate members between a collection of elements and relativemovement between elements unless otherwise indicated. The exemplarydrawings are for purposes of illustration only and the dimensions,positions, order and relative sizes reflected in the drawings attachedhereto can vary. As used herein, the term “set” or a set of an articleshould be understood to include any number of said article, includingonly one.

Referring now to FIG. 1, an aircraft 10 includes a pair of heatexchangers 12 (shown in dashed line), which are arranged in in a pair ofaircraft engines 14 mounted to the aircraft 10. The heat exchangers 12aid in dissipating the heat generated by the engines 14. It should beunderstood that the heat exchangers 12 can be located anywhere withinthe aircraft 10, not just within the engines 14 as illustrated. Forexample, there can be any number of heat exchangers arranged around theaircraft 10 at any position. While illustrated in a commercial airliner,the heat exchangers 12 can be used in any type of aircraft, for example,without limitation, fixed-wing, rotating-wing, rocket, commercialaircraft, personal aircraft, and military aircraft. Furthermore, aspectsof the disclosure are not limited only to aircraft aspects, and can beincluded in other mobile and stationary configurations. Non-limitingexample mobile configurations can include ground-based, water-based, oradditional air-based vehicles. Any implementation has its own spaceconstraints and temperature or operational requirements. As such, thedesign of the particular aspects of the heat exchanger 12 as describedherein can be tailored to suit specific installation requirements of theimplementation.

Referring now to FIG. 2, the heat exchanger 12 can include a heatexchanger core 16 defining an inner section 20, and including walls as afirst side 22, a second side 24, a third side 26, and a fourth side 28.A first set of flow passages 30 extending from the first side 22 to thesecond side 24. A second set of flow passages 34 can extend from thethird side 26 to the fourth side 28. The first set of flow passages 30can be thermally coupled with the second set of flow passages 34, suchas being intertwined with one another. Such an intertwining of the firstand second sets of flow passages 30, 34 can be complex, with amulti-faceted, convoluted geometry made from additive 3D metal printing,for example. In other example, the flow passages could betreacherous-path or diabolically convoluted geometries. Alternatively,other suitable methods of forming the core 16 having the first andsecond sets of flow passages 30, 34 are contemplated, such as casting inone non-limiting example. As such, the heat exchanger core 16 can beconsidered as a monolithic block or monolithic core for the heatexchanger 12. The core 16 is preferably made of a material having a highheat transfer coefficient to facilitate transfer of heat between thefirst set of flow passages 30 and the second set of flow passages 34.One such suitable material can be aluminum, for example. For hightemperature applications, nickel and cobalt alloys are possiblealternatives.

An outer housing, walls, or skin 18 can surround the core 16. A set offlanges 32 can extend from the skin 18, and can include apertures 36provided in the flanges 32. While not shown, one or more load paths canbe included with the skin 18, adapted to receive physical or thermalloads during operation of the heat exchanger 12. Such load paths can beformed in the inner section 20, and can be dependent on the geometry ofthe core 16, or the first or second sets of flow passages 30, 34. Theskin 18 can couple to and share such load paths. It is furthercontemplated that the skin 18 can include additional structures adaptedto form the load path along or through the core 16 for carrying astructural or thermal load. Thus, the skin 18 can form the structuralboundary for carrying the heat exchanger core 16, and can at leastpartially surround the core 16, or surround only a portion of the core16. In one example, the skin 18 can be integral with the core 16. Theskin 18, including the outer housing or outer walls and any structuralload paths forming the skin 18, can be made of a high tensile strengthiron-nickel alloy, having a percentage or nickel concentration tailoredto determine a coefficient of thermal expansion for the skin 18 relativeto an anticipated operational temperature for the core 16.

A set of manifolds 40, shown as four manifolds 40, can couple to thecore 16 or the optional outer housing 18 or skin 18 to provide foringress and egress of fluid to the core 16. More specifically, the setof manifolds 40 can provide for ingress and egress of fluid to the firstand second sets of flow passages 30, 34. Each manifold 40 can include aninlet plane 56 and an outlet plane 58, providing for ingress or egressof fluid to or from the manifold 40. The set of manifolds 40 can providefor ingress and egress of fluid to the first and second sets of flowpassages 30, 34 via the inlet plane 56 or the outlet plane 58. As such,for a manifold 40 having a flow entering the first and second sets offlow passages 30, 34, the inlet plane 56 is spaced from the core 16,while the outlet plane 58 can be adjacent the core 16. Similarly, butopposite, a manifold 40 providing for flow coming from the first andsecond sets of flow passages 30, 34, the inlet plane 56 can be adjacentthe core 16, while the outlet plane 58 can be spaced from the core 16.It should be understood that “plane” as used herein, in regards to aninlet plane 56 and an outlet plane 58, should not necessarily representa geometrical plane or mean geometrically planar, but rather berepresentative of a boundary or threshold defining an inlet or an outletfor a referenced manifold 40, and can be relative to flow directionthrough the manifold 40. While shown as having a substantially curved,conic body, with a cylinder extending from the body, it should beunderstood that any suitable geometry for the set of manifolds 40 iscontemplated.

Referring now to FIG. 3, the set of manifolds 40 can include a firstinlet manifold 42, a first outlet manifold 44, a second inlet manifold46, and a second outlet manifold 48. One or more manifolds of the set ofmanifolds can be unitary with or integral with the core 16, formed as aunitary body with the core, or formed as an single whole. A set ofmounting flanges 62 can couple to the set of manifolds 40. The mountingflange 62 can mount to a fixed structure for mounting the heat exchanger12, such as to a portion of the engine 14 of FIG. 1.

The first inlet manifold 42 couples to the core 16 adjacent the firstset of flow passages 30 at the first side 22. A rib 50 can extend fromthe first inlet manifold 42 to the core 16. While only shown as a singlerib 50, any number of ribs 50 or similar in-situ structures can beutilized with any manifold 40 described herein adapted to improvestructural integrity of the manifolds 40.

A first inlet 60 can be formed in the first inlet manifold 42, spacedfrom the first set of flow passages 30. One or more sidewalls 64 can atleast partially form the first inlet manifold 42 can extend between themounting flange 62 and the core 16, defining an interior 66 for thefirst inlet manifold 42. The first inlet manifold 42 can be made ofnickel, nickel-cobalt, or a nickel alloy, in non-limiting examples. Inone example, the first inlet manifold 42 can be made of an iron-nickelalloy, and can be manufactured to have a specific percentage of nickel,or nickel concentration. Such material provides for a high tensilestrength, while having a coefficient of thermal expansion (CTE) that isless than that of the core 16. Particularly, such materials can providefor increased strength and impact resistance up to 600 degreesFahrenheit (F.), while more particularized alloys can provide fortemperatures up to 1000 degrees F. or more.

The first outlet manifold 44 is fluidly coupled to the core 16 adjacentthe first set of flow passages 30 at the second side 24. A first outlet80 can be formed in the first outlet manifold 44, spaced from the firstset of flow passages 30. The first outlet manifold 44 can be positionedopposite of the first inlet manifold 42, relative to the core 16, andcan fluidly couple to the first inlet manifold 42 via the first set offlow passages 30. The first outlet manifold 44 can include a sidewall 82and geometry similar to that of the first inlet manifold 42. Similar tothe first inlet manifold 42, the first outlet manifold can be made ofnickel, nickel-cobalt, or a nickel alloy such as iron-nickel, innon-limiting examples.

A second inlet manifold 46 couples to the core 16 adjacent the secondset of flow passages 34 at the third side 26. A second inlet 70 can beformed in the second inlet manifold 46, and can be spaced from thesecond set of flow passages 34. A first sidewall 72 can extend from thecore 16 to a second sidewall 74. The second sidewall 74 can be arrangedsubstantially orthogonal to the first sidewall 72; however, anyorientation is contemplated. The first and second sidewalls 72, 74 canat least partially define an interior 76 for the second inlet manifold46. Similarly, the second inlet manifold 46 can be made of aniron-nickel alloy, and can be manufactured to have a specific percentageof nickel, or nickel concentration.

The second outlet manifold 48 couples to the core 16 adjacent the secondset of flow passages 34 at the fourth side 28. A second outlet 84 can beformed in the second outlet manifold 48, and can be spaced from thesecond set of flow passages 34. The second outlet manifold 48 can bepositioned opposite of the second inlet manifold 46 relative to the core16, and can fluidly couple to the second inlet manifold 46 via thesecond set of flow passages 34. It is further contemplated that thesecond outlet manifold 48 can include one or more compliant features.

It should be appreciated that the organization for the heat exchanger 12and manifolds 40 as shown are exemplary, and that any suitable geometryfor the core 16 that provides for a heat exchange between a hot fluidand a cold fluid can form the suitable heat exchanger 12. It should beunderstood that the manifolds 40 have been illustrated merely forexemplary purposes and can include any suitable shape, profile,arrangement, or attachments for effectively providing one or more fluidsto, and removing one or more fluids from the heat exchanger 12 or thecore 16.

During operation, a first fluid can be provided through the core 16along the first set of flow passages 30, such as a hot fluid. Therefore,the first inlet manifold 42, the first set of flow passages 30, and thefirst outlet manifold 44 can form a hot fluid path. The first inlet 60can be a hot inlet and the first outlet 80 can be a hot outlet.

A second fluid can be provided through the core 16 along the second setof flow passages 34, such as a cold fluid. Therefore, the second inletmanifold 46, the first set of flow passages 34, and the first outletmanifold 44 can form a cold fluid path. The second inlet 70 can be acold inlet and the second outlet 84 can be a cold outlet.

During simultaneous flow of the hot fluid and the cold fluid, a heatexchange takes place within the core 16, cooling the hot fluid andheating the cold fluid. An average of the temperatures between the hotfluid and the cold fluid within the core 16 can define a meantemperature for fluids passing through the core 16. Dependent on thetemperatures of the hot and cold fluids, a large temperature difference,or temperature gradient, can exist between the mean temperature of thecore 16 and the hot or cold fluids at the first and second inletmanifolds 42, 46, respectively. Resultant of increasing or decreasingtemperatures in the core 16, thermal expansion and contraction of thecore 16 can occur. Such expansion and contraction of the structurallyrigid core 16 can cause thermal stresses at the junction between thecore 16 and the manifolds 40. An additional and superimposed hightemperature gradient condition can occur between a local hot section ofthe core adjacent to the cold inlet manifold fluid. A significanttemperature gradient exists at this location. An opposite and similarcondition exists at a local region between a cold fluid passage of thecore and the hot inlet manifold fluid. The thermal stresses can be theresult of the significant temperature change of the core 16 resulting inthermal expansion. Such thermal or structural stresses can result infracture or deformation of the heat exchanger 12, which can reducecomponent life or require increased maintenance. Furthermore, suchthermal stresses can be exacerbated due to a structurally stiff core 16,resultant of the complex geometry of the first and second sets of flowpassages 30, 34 forming the core 16.

Additionally, thermal expansion of the core 16 can cause physicalstresses at the junction between the manifolds 40 and the mountingflanges 62. As a result, the structurally stiff mounting flange 62 canbe particularly susceptible to damage or deformation due to theincreased combined thermal and structural or physical stresses.

Referring now to FIG. 4, a plot graph 100 illustrates five plots forfive different operation temperatures for a heat exchanger, showing aCTE as parts per million per degrees Celsius (ppm/° C.), on the y-axis,plotted against an atomic percentage of nickel on the x-axis. Such anatomic percentage can be the percentage of nickel in an iron-nickelalloy, for example, which can be utilized to form the heat exchanger 12or a portion thereof such as a manifold 40.

A first plot 102 illustrates an operational temperature for a manifoldhaving a fluid at a temperature of 15 degrees Celsius (° C.). As isappreciable, the CTE for the first plot 102 is at a minimum betweenabout 30-45 atomic percent nickel, shown as below 5 ppm/° C.

A second plot 104 illustrates an operational temperature for a manifoldhaving a fluid at a temperature of 200° C. The CTE for the second plot104 is at a minimum between about 35-42 atomic percent nickel, shown asbetween 4 and 7 ppm/° C.

A third plot 106 illustrates an operational temperature for a manifoldhaving a fluid at a temperature of 300° C. The CTE for the third plot106 is at a minimum between about 38-50 atomic percent nickel, shown asbetween 7-10 ppm/° C.

A fourth plot 108 illustrates an operational temperature for a manifoldhaving a fluid temperature of 400° C. The CTE for the fourth plot 108 isat a minimum between about 45-55 atomic percent nickel, shown as between8-10 ppm/° C.

A fifth plot 110 illustrates an operational temperature for a manifoldhaving a fluid temperature of 500° C. The CTE for the fifth plot 110 isat a minimum between about 50-55 atomic percent nickel, shown as between11-13 ppm/° C.

Therefore, a range 112 between about 38-50 atomic percent nickel for analloy can provide for reducing a CTE over a wide range of operationaltemperatures, from about 0° C. to 500° C. Therefore, the manifold 40having a percent nickel between about 38-50 percent can be utilized in awide range of operational conditions or systems. However, it iscontemplated that the manifold 40 can have a specific atomic percentnickel tailored to a specific manifold temperature or fluid temperature.For example, in a heat exchanger 12 expected to operate at 200° C., amanifold 40 having about 38 atomic percent nickel could be utilized tooperate having a CTE of about 4 ppm/° C. As such, a range of 35-55percent nickel or 40-50 percent nickel may be utilized to cover a widerange of operational temperatures, with more specific tailoring of thepercent nickel directed to the specific temperature of theimplementation. Smaller ranges such as 38-50 percent, or 40-50 percentnickel are also contemplated, or even smaller ranges tailored to asingle operational temperature, such as between 35-40% nickel for a 200°C. operation temperature.

Without such tuning severe negative effects can occur due to thetemperature gradient between the core 16 and the manifolds 40, the highstructural stiffness of the monolithic core 16, and the rigid housingconnections to adjacent fixed boundary conditions such as the mountingflanges 62. For example, during thermal growth of the core 16, the loadpath along the core at the manifolds 40 can cause localize thermalstresses which can lead to damage or low cycle fatigue fracturing of theheat exchanger 12. Similarly, the mounting flanges 62 for the heatexchanger 12 can be susceptible to thermal growth of the manifolds 40,which can lead to physical stresses at the mounting flanges 62, whichcan otherwise result in damage or fracturing of the heat exchanger 12.

The reduced CTE for the skin 18 or the manifolds 40 results in inreduced thermal growth of that portion of the heat exchanger 12. Itshould be appreciated that utilizing the nickel alloy having a specificatomic percent of nickel can tailored to have a reduced CTE, lesser thatthat of the core 16. The reduced CTE can be tailored based uponanticipated operational temperatures of the heat exchanger 12, themanifolds 40, or to a temperature gradient between the core 16 and themanifolds 40 or the skin 18. Utilizing the nickel alloys to reduce theCTE to be less than the core 16 can provide for reducing local thermalstresses at the manifolds 40 or the skin 18, especially at the mountingflanges 62 for mounting the heat exchanger 12. It should be appreciatedthat similar materials are contemplated, such as similarelectrodeposited metal alloys having a reduced CTE. Such similar alloyscan have unique percentages of the respective alloys to reduce the CTEbased upon the anticipated operational temperatures of the heatexchanger or the temperature gradient with the core 16. Furthermore, thenickel alloys can provide for a high tensile strength. The high tensilestrength can be better suited to the thermal stresses during operationof the heat exchanger 12, which can provide for increased componentlifetime and reduced maintenance.

Referring now to FIG. 5, a flow chart shows a method 150 of forming aheat exchanger, such as the heat exchanger 12 described herein. Themethod 150 begins at 152 with forming the monolithic core, such as thecore 16. This can be done utilizing additive manufacturing or 3Dprinting. For example, the core 16 can be formed utilizing direct metallaser melting (DMLM) or direct metal laser sintering (DMLS). Forming thecore 16 can include at least a first set of flow passages, such as theflow passages 30 as described herein. Such formation can form amonolithic core 16, having the first and second sets of flow passages30, 34 defined through the core 16. Additionally, such techniques canprovide for the complex geometries or organizations of the first andsecond flow passages 30, 34, facilitating heat exchange between fluidspassing therethrough. In one example, the core 16 can be formed withaluminum. The core 16 can be have a first coefficient of thermalexpansion, or can be made of a material having a first coefficient ofthermal expansion. In one example, the core 16 can be made of a firstmaterial, such as aluminum, where the first coefficient of thermalexpansion is greater than 20 ppm/° C., such as 24 or 25 ppm/° C.

Optionally, at 154 at least a portion of the skin 18 can be additivelymanufactured onto the core 16. By way of non-limiting example, the skin18 can have a coefficient of thermal expansion that is less than thecoefficient of thermal expansion of the core 16. The skin 18 can beformed by electroforming or electroplating. For example, the skin 18 canbe formed of a Ni-Fe alloy having between 35-55% nickel, or 40-50%nickel, while any suitable concentration or range thereof based uponanticipated operating temperatures is contemplated. In one example, theskin 18 can be integrally formed onto the core 16.

At 156, a first manifold, such as the first inlet manifold 42, or a hotinlet manifold, can be additively manufactured onto the core 16. Suchformation can form a unitary body as the combined core 16 and the firstmanifold, or a unitary body as the combined core 16, skin 18, and thefirst manifold. Additive manufacturing can include electroforming,electroplating, DMLM, or DMLS, for example, and can be controlled usingdirect or pulsed current power supplies. The first inlet manifold 42 candefine a first fluid inlet, such as the first inlet 60, which is influid communication with the first set of flow passages 30. At least aportion of the first inlet manifold 42 can be formed of a secondmaterial, such as the Ni-Fe alloy, that has a coefficient of thermalexpansion that is different than or less than a coefficient of thermalexpansion of the core 16. For example, the Ni-Fe alloy can include anatomic percentage of nickel that is between 35-55% nickel, or 40-50%nickel, or having a coefficient that is between 5-10 ppm/° C.Alternatively, other percentages of nickel are contemplated, beingspecifically tailored to a particular anticipated heat exchangeroperational temperature or temperature gradient. A coefficient ofthermal expansion of 5-10 ppm/° C. is different from and less than thatof the core 16 having a first material as aluminum, having a coefficientof thermal expansion that is about 24 ppm/° C. The lesser coefficient ofthermal expansion for the first inlet manifold 42 can reduce thermalstresses at the first inlet manifold 42. It is further contemplated thata first portion of the first inlet manifold 42 can be formed to have afirst coefficient of thermal expansion and a second portion of the firstinlet manifold 42 can be formed to have a second coefficient of thermalexpansion different than the first portion, where both portions have acoefficient of thermal expansion that is less than that of the core 16.

Optionally, at 156, a second manifold, such as the second inlet manifold46, or a cold inlet manifold, can be additively manufactured onto thecore 16. The second manifold and the core 16, or the skin 18, or both,can be formed as a unitary body. The second manifold can define a secondfluid inlet that is in communication with the second set of flowpassages 34. Similar to the first inlet manifold, the second manifoldcan be made of a second material, or even a third material, such as atleast a portion of the second manifold formed having the Ni-Fe alloy andcan include an atomic percentage of nickel that is between 35-55% or40-50%, to have a coefficient of thermal expansion for the secondmanifold that is less than that of the core 16. Such manufacturing caninclude electroforming or electroplating, and can include controlleddirect or pulsed current power supplies. Furthermore, the secondmanifold can have a coefficient of thermal expansion that is differentthan that of the first inlet manifold, such as having a coefficient ofthermal expansion that is different from, greater, or lesser than thefirst inlet manifold, while still less than that of the core 16.

It should be appreciated that the heat exchanger 12 can be formedutilizing additive manufacturing, utilizing one or more method such asdirect metal laser melting (DMLM), direct metal laser sintering (DMLS),electroforming, or electroplating, in non-limiting examples. Suchformation can utilize controlled direct or pulsed current power suppliesto determine a local concentration of material, such as a nickelconcentration in a Fe-Ni alloy. Furthermore, separate portions of theheat exchanger 12 can be formed utilizing different method of additivemanufacturing. For example, the core 16 can be formed by DMLM, while themanifolds 40 are formed using electroforming. Such methods enable a core16 that has a high heat transfer coefficient, while the manifolds 40 canbe made having a low CTE.

Referring now to FIG. 6, the core 16, shown as including the skin 18,can have been previously formed utilizing DMLM or DMLS, for example. Thecore 16 can then be placed in a bath tank 120. A metal constituentsolution 122 can fill the bath tank 120. The metal constituent solution122 can, by way of non-limiting example, be a nickel alloy as describedabove including a Ni-Fe alloy or nickel carrying iron ions. An anode 124can be provided in the bath tank 120. The anode 124 can be a sacrificialanode or an inert anode, for example. The heat exchanger 12 can form acathode 126, or multiple cathodes 126 along separate surfaces of theheat exchanger 12. As shown, at least a portion of the skin 18 can forma cathode surface 126, where the skin 18 is formed as having anickel-iron (Ni-Fe) alloy, surrounding at least a portion of the core16.

Electrical conduits 128 couple the anode 124 and the cathodes 126 to acontrolled direct or pulsed current power supply 130, which can controlelectroforming or electroplating of the Ni-Fe portions of the heatexchanger 12. For example, the current provided to the bath tank 120 cancontrol the rate of electroforming, or can even be used to determine theconcentration of nickel formed onto the heat exchanger 12.

Referring now to FIG. 7, sacrificial manifold molds 132 can be providedon the core 16. The sacrificial manifold molds 132 can be made of anelectrically conductive material permitting electroforming orelectroplating at the sacrificial manifold molds 132. The remainingportions of the core 16 or the skin 18 can be prepared, such as coveredwith a non-conductive material to prevent electroforming onto theremainder of the core 16. Electrical conduits 128 can be coupled to thesacrificial manifold molds 132, utilizing the sacrificial manifold molds132 as cathodes 126 to electroform the manifolds 40 to the core 16. Thepower supply 130, also coupled to the anode 124, can controlelectroforming or electroplating of the manifolds 40 to the core 16.

In one alternative example, a sacrificial mold can be made for the skin18 in addition to the sacrificial manifold molds 132. As such, both theskin 18 and the manifolds 40 can be formed integrally and simultaneouslywith one another.

Referring now to FIG. 8, the manifolds 40 can be completely formed tothe core 16, forming the heat exchanger 12, having the heat exchanger 12removed from the bath tank 120 of FIGS. 5 and 6. The manifolds 40 areformed of the Ni-Fe alloy, and can have a predetermined atomicpercentage of nickel, which can be used to reduce the CTE for themanifolds 40, such that the CTE for the manifolds 40 is less than thatof the core 16. As such, the core 16 can be made of a material havinghigh thermal conductivity, such as Aluminum, while the manifolds 40 aremade of a material having a lesser CTE. The lesser CTE for the manifolds40 reduces local thermal stresses of the heat exchanger 12 caused byexpansion of the core 16 during operation of the heat exchanger.

It should be appreciated that as described herein, forming at least aportion of one or more heat exchanger manifolds, or the skin, or forminga load-bearing portion of the heat exchanger with a nickel alloy havinga particular atomic percentage of nickel can be used to tune thecoefficient of thermal expansion for that portion of the heat exchanger.More specifically, that portion of the heat exchanger can be formed tohave a CTE that is less than that of the core or another portion of theheat exchanger. In some examples, the CTE for the manifold or the skincan be less than 15 ppm/° C., or even can be less than 10 ppm/° C.,while an Aluminum core can have a CTE of 24 ppm/° C., for example.

Aspects of the present disclosure allow for a monolithic core formed ofmaterials such as aluminum while having integral manifolds and skinformed of metal alloys having a lower CTE. This can result in reducedthermal stresses at the heat exchanger resultant of thermal growthduring operation of the heat exchanger, which can lead to reduced damageto the heat exchanger and increased operational life, with reducedmaintenance. Furthermore, utilizing the nickel alloys for the manifoldor skin can result in portions of the heat exchanger having increasedtensile strength, as compared to the materials utilized in the core. Forexample, the FeNi alloy can have an ultimate tensile strength of 500-900megapascals (MPa). Therefore, it should be appreciated that the CTE andthe tensile strength of the manifolds or the skin can be tuned by thepercentage of nickel included in the electroformed alloy.

The heat exchangers as described herein can be made with additivemanufacturing, such as electroforming the manifolds or the skin havingthe predetermined atomic percentage of nickel onto the core. Suchmanufacturing provides for precise forming of the manifolds or the skinhaving the particular desired atomic percentages of nickel.

Additionally, it should be appreciated that the elements describedherein that are additively manufactured, such as the core 16, the skin18, and the manifolds 40, can include in-situ features to furtherincrease local structural strength of the heat exchanger 12. Forexample, ribs or iso-grids can be additively manufactured at high stresslocations in order to provide additional strength or structuralintegrity. Such in-situ features can improve lifetime of the heatexchanger 12 and reduce required maintenance.

This written description uses examples to describe aspects of thedisclosure described herein, including the best mode, and also to enableany person skilled in the art to practice aspects of the disclosure,including making and using any devices or systems and performing anyincorporated methods. The patentable scope of aspects of the disclosureis defined by the claims, and may include other examples that occur tothose skilled in the art. Such other examples are intended to be withinthe scope of the claims if they have structural elements that do notdiffer from the literal language of the claims, or if they includeequivalent structural elements with insubstantial differences from theliteral languages of the claims.

To the extent not already described, the different features andstructures of the various aspects may be used in combination with eachother as desired. That one feature may not be illustrated in all of theaspects is not meant to be construed that it may not be, but is done forbrevity of description. Thus, the various features of the differentaspects may be mixed and matched as desired to form new aspects, whetheror not the new aspects are expressly described. All combinations orpermutations of features described herein are covered by thisdisclosure.

What is claimed is:
 1. A method of forming a heat exchanger, the methodcomprising: forming a monolithic core having a first set of flowpassages; and additively manufacturing onto the monolithic core a firstmanifold, where the first manifold defines a first fluid inlet that isin fluid communication with the first set of flow passages and at leasta portion of the first manifold has a coefficient of thermal expansionless than a coefficient of thermal expansion of the monolithic core. 2.The method of claim 1 wherein the monolithic core and the first manifoldare formed as a unitary body.
 3. The method of claim 1 wherein themonolithic core is made of a first material and the first manifold ismade of a second material different from the first material.
 4. Themethod of claim 3 wherein the second material is a nickel alloy having35-55% nickel.
 5. The method of claim 4 wherein the first material isaluminum.
 6. The method of claim 1 wherein additively manufacturingincludes electroforming.
 7. The method of claim 6 wherein electroformingincludes utilizing a controlled direct or pulsed current power supply.8. The method of claim 6 wherein forming the monolithic core includesdirect metal laser melting or direct metal laser sintering.
 9. Themethod of claim 1 wherein forming the monolithic core further includes asecond set of flow passages fluidly separate from the first set of flowpassages.
 10. The method of claim 9, further comprising additivelymanufacturing onto the monolithic core a second manifold, where thesecond manifold defines a second fluid inlet that is in fluidcommunication with the second set of flow passages and where the secondmanifold has a coefficient of thermal expansion less than thecoefficient of thermal expansion of the monolithic core.
 11. The methodof claim 10 wherein the coefficient of thermal expansion of the firstmanifold is different from the coefficient of thermal expansion of thesecond manifold.
 12. The method of claim 1, further comprisingadditively manufacturing onto at least a portion of the monolithic corea skin and where the skin has a coefficient of thermal expansion lessthan the coefficient of thermal expansion of the monolithic core. 13.The method of claim 1 wherein the first manifold is made of aniron-nickel alloy.
 14. A method of forming a heat exchanger, the methodcomprising: forming a monolithic core having a first set of flowpassages from a first material having a first coefficient of thermalexpansion; and additively manufacturing a first manifold from a secondmaterial different than the first material onto the monolithic core influid communication with the first set of flow passages having a secondcoefficient of thermal expansion lower than the first coefficient ofthermal expansion; wherein the second material is a nickel alloy havingbetween 35-55% nickel.
 15. The method of claim 14 wherein the nickelalloy has between 40-50% nickel.
 16. The method of claim 14 whereinforming the monolithic core includes one of direct metal laser meltingor direct metal laser sintering, and additively manufacturing the firstmanifold includes electroforming the first manifold.
 17. The method ofclaim 16 wherein the monolithic core and the first manifold are formedas a unitary body.
 18. The method of claim 14 further comprisingadditively manufacturing a skin onto the monolithic core, with the skinmade of the nickel alloy having between 35-55% nickel.
 19. A heatexchanger, comprising: a monolithic core body having a first set of flowpassages and a first coefficient of thermal expansion; and a firstmanifold unitarily formed with the monolithic core body in fluidcommunication with and defining a first fluid inlet for the first set offlow passages, and having a second coefficient of thermal expansion thatis different than the first coefficient of thermal expansion.
 20. Theheat exchanger of claim 19 wherein the first coefficient of thermalexpansion is less than the second coefficient of thermal expansion. 21.The heat exchanger of claim 19 further comprising a skin surrounding atleast a portion of the monolithic core body having a coefficient ofthermal expansion that is less than the coefficient of thermal expansionof the monolithic core body.
 22. The heat exchanger of claim 19 whereinthe first manifold is made of a nickel alloy having between 35-55%nickel.
 23. The heat exchanger of claim 19 wherein the at least aportion of the first manifold includes a coefficient of thermalexpansion ranging from 5 to 10 ppm/° C.
 24. The heat exchanger of claim23 wherein the first coefficient of thermal expansion is greater than 20ppm/° C.